(294d) A Novel Artificial Antibody for Reversible Cell Recognition

Antibodies have been widely used in cell separation applications. However, the strong interactions between antibodies and cell receptors can cause undesired intracellular signaling cascades or even the death of cells. In addition, the antibody-based applications are usually limited due to their fragile structures and irreversible denaturation. For instance, random chemical conjugation in the variable region of an antibody can lead to a significant loss of its binding ability. Therefore, it is highly desirable to develop antibody mimics that not only possess the molecular recognition capability of antibodies, but also have specific features that natural antibodies do not have. In this research, a novel artificial antibody was synthesized with two nucleic acid aptamers and a dendrimer. The aptamers were used to mimic the antigen-binding sites of an antibody. The dendrimer was used as a nanoscaffold to provide a defined chemical conjugation site. Nucleic acid aptamers are single-stranded oligonucleotides that are selected from oligonucleotide libraries containing up to 10¹⁴-10¹⁵ random DNA or RNA sequences. Nucleic acid aptamers have high binding affinity and specificity. In addition, aptamers can be chemically functionalized to achieve high stability. Interestingly, the binding functionality of aptamers can be tuned by changing the environmental conditions such as temperature. Dendrimers are spherical nanostructures with multiple surface groups. Dendrimers have been widely used as a nanoscaffold in numerous applications such as cell labeling and drug delivery. The properties and functionality of this artificial antibody were characterized by numerous assays. Dynamic light scattering was first performed to characterize the size of the artificial antibody. The result showed that its D_h was ~12.8 nm, which is virtually the same as that of an IgG. Three cell assays were further applied to evaluate its binding ability. The first one was to test its capability in binding target cells. The results showed that the binding of the artificial antibody reached plateau at a concentration of 50 nM. In addition, the binding strength of the bivalent artificial antibody was much higher than its monovalent control. The second assay was a passive dissociation experiment. The target cells were first labeled by different concentrations of nanomaterials and then subjected to a 30-min passive dissociation. The dissociation of the artificial antibodies was almost negligible while the majority of the monovalent nanomaterials were dissociated from the cell surface. In the third cell assay, we studied the dissociation of the artificial antibodies from cell surface in response to a temperature shift. The strong binding of the artificial antibodies to target cells could be reversed by a temperature shift from 0 ºC to 37 ºC. Taken together, our data showed that this biomimetic nanomaterial holds great potential for the development of bioseparation or diagnostic devices. (This research is supported by grants from the NSF (DMR-0705716) and the UConn Research Foundation.)